[Gretl-devel] increment and decrement operators

Hello all + season's greetings Up till now gretl has supported only very limited usage of the increment (++) and deccrement (--) operators. The only acceptable usage has been in stand-alone expressions (e.g.) j++ # shorthand for j = j + 1 j-- # shorthand for j = j - 1 for "j" the name of a user-defined scalar variable. As of today's CVS I'm experimenting with fuller support for something that is really quite handy in C and similar languages, namely the ability to embed constructs such as "j++" and "j--" in more or less arbitrary contexts. For example: k = j++ # k = current value of j; then increment j m[j++] = x # assign x to element j of m; increment j x = foo(j--) # evaluate foo(j); decrement j Two limitations: (1) only named scalars are supported in this way; and (2) only the "postfix" variant is supported -- where the scalar variable in question is incremented or decremented after its value is taken, unlike C where you can also use "++j" and "--j" to increment or decrement j before its value is taken. If people can test this, that would be very helpful. Since gretl also supports the "unary +" operator there's a potential ambiguity over what "++" means. The expression x++2 is equivalent to "x + (+2)" or just "x + 2". However, I believe we're OK: contexts where "++" should be interpreted in this way can be distinguished syntactically from contexts where "evaluate then increment" is warranted. If anyone finds a case where they think "++" (or "--") is being interpreted wrongly, please let me know. FYI: it's in CVS but not yet in snapshots. Allin Cottrell